Most European countries use the Global System for Mobiles or GSM network, as do a whole heap of other countries around the world. This is one of the main reasons why, as long as your phone is operating on the same network, you shouldn't come across any usage issues when travelling.

Yes, you can absolutely use a US phone in Europe in 2026, but the "how" depends on your carrier and your device's compatibility. Most modern US smartphones (iPhone 12 and newer, or recent Samsung Galaxy models) are "Global" or GSM-compatible, meaning they support the frequency bands used by European networks. To use your phone, you have three main options: 1) International Roaming, where carriers like AT&T or Verizon charge a daily fee (often $10–$12) to use your domestic plan; 2) eSIM, which is the most popular choice in 2026—you can download an app like Airalo or Holafly to get a local data-only plan instantly; or 3) Local Physical SIM, though this requires your phone to be "Unlocked" by your US carrier. It is important to check if your phone is "SIM Locked" in your settings before you travel. Also, remember that while your phone will work for data, you may need to use apps like WhatsApp or FaceTime for calls to avoid high international per-minute rates, as US numbers roaming in Europe are often treated as "international long distance" for traditional voice calls.